Copper is a durable and adaptable material that is used to make long-lasting roofs and gutters. Over time, it accumulates a hard layer of oxidized copper which appears blue-green to deep-brown and can be seen on international icons like The Statue of Liberty or bronze statues such as Rodin's The Thinker.
When you think of copper, do you think of a shiny orange penny?
Or do you think of the seafoam green Statue of Liberty?
When looking at both side by side, it’s hard to fathom that both are made of the same material. Copper starts off as the orange-bronze color seen on a new penny. Over time, it then natural begins to change color, this is oxidation at work and the result is patina. Patina is the film that is created on the surface of copper and is caused by air exposure and oxidation. As time goes on, this layer thickens, protecting the underlying copper from damage.
Thanks to patina, copper can change from the normal russet brown to dark brown, green, and the famous turquoise color that can be seen on the Statue of Liberty.
(Pictured: Bad Doberan, MV, Germany)
The local climate and environment influence how fast copper oxidizes. For copper to patina, it needs moisture to create the corrosive barrier. Copper in humid environments, such as Florida, will oxidize more quickly than drier climates, such as Nevada. Airborne pollutants can also accelerate oxidation.
For example, regions with precipitation of a pH less than 5.5 will age copper more quickly than alkaline climates. Areas with heavy industrial pollutants or salty marine environments will also quicken this process. Not all contributing factors affect the copper equally, causing patina to accumulate unevenly or produce a different color.
Over time, this process will even out, making the copper more uniform in color and texture.
(Pictured: The Thinker, Rodin Museum, Paris, France)
It is uncertain how long it took for the Statue of Liberty to patina, but the process was likely sped up by the nearby water and centuries of pollution. Lady Liberty is exposed to all types of weather, pollution, and water. Taken together, this American icon is a stand-out demonstration of copper's longevity and durability. She was renovated 100 years after being built and has needed very little maintenance work throughout the years.
Because the natural oxidation process varies, patina formation can be accelerated for design purposes.
For our project at the Norwegian Embassy, pre-patinaed copper was purchased because it was the final design of the building. The pre-patinaed copper was necessary in this case because it was a salute to the Statue of Liberty’s copper coming from the mine in the village of Visnes, Norway.
(Pictured: Close-up of copper panels, Norwegian Embassy, Washington DC)
Scrubbing the copper material (or pressure washing it) will disturb the naturally accumulated patina, diminishing the protection it provides. Aggressive cleaning will only delay the oxidation process, not stop it, and may damage the soft copper material, its expert installation, resulting in real damage or an uneven and unsightly patina.